Re: [PATCH V2] arm64: hwpoison: add VM_FAULT_HWPOISON[_LARGE] handling

[Baicar, Tyler]

On 3/7/2017 12:56 PM, Punit Agrawal wrote:
> Punit Agrawal <punit.agrawal@xxxxxxx> writes:
>
> [...]
>
> > The code looks good but I ran into some failures while running the
> > hugepages hwpoison tests from mce-tests suite[0]. I get a bad pmd error
> > in dmesg -
> >
> > [  344.165544] mm/pgtable-generic.c:33: bad pmd 000000083af00074.
> >
> > I suspect that this is due to the huge pte accessors not correctly
> > dealing with poisoned entries (which are represented as swap entries).
> I think I've got to the bottom of the issue - the problem is due to
> huge_pte_at() returning NULL for poisoned pmd entries (which in turn is
> due to pmd_present() not handling poisoned pmd entries correctly)
>
> The following is the call chain for the failure case.
>
> do_munmap
>    unmap_region
>      unmap_vmas
>        unmap_single_vma
>          __unmap_hugepage_range_final    # The test case uses hugepages
>            __unmap_hugepage_range
>              huge_pte_offset             # Returns NULL for a poisoned pmd
>
> Reverting 5bb1cc0ff9a6 ("arm64: Ensure pmd_present() returns false after
> pmd_mknotpresent()") fixes the problem for me but I don't think that is
> the right fix.
>
> While I work on a proper fix, it would be great if you can confirm that
> reverting 5bb1cc0ff9a6 makes the problem go away at your end.
Thanks Punit! I haven't got a chance to do this yet, but I will let you 
know once I get it tested :)
> > I am investigating the failure but could you try running the tests at
> > your end as well.
> >
> > To run the tests, I cloned the repository[0]. It test needs a simple fix
> > at the end of this mail to run correctly. With that applied and running
> > as root -
> >
> > # cd mce-test/cases/function/hwpoison
> > # ./run_hugepage.sh
> >
> >
> > [0] https://git.kernel.org/cgit/utils/cpu/mce/mce-test.git/
> >
> > --------->8--------------
> > commit cb5c61f18dd86baf01b90404d4ecf51dd3d176c7
> > Author: Punit Agrawal <punit.agrawal@xxxxxxx>
> > Date:   Thu Mar 2 18:24:40 2017 +0000
> >
> >      Use correct return type for getopt_long
> >
> >      getopt_long returns an int. Fix the return type to avoid issues when
> >      checking for negative error codes on architectures with unsigned char,
> >      e.g., arm.
> >
> >      Signed-off-by: Punit Agrawal <punit.agrawal@xxxxxxx>
> >
> > diff --git a/cases/function/hwpoison/thugetlb.c b/cases/function/hwpoison/thugetlb.c
> > index 92dc7d2..fbcf426 100644
> > --- a/cases/function/hwpoison/thugetlb.c
> > +++ b/cases/function/hwpoison/thugetlb.c
> > @@ -125,7 +125,7 @@ int main(int argc, char *argv[])
> >          int forkflag = 0;
> >          int privateflag = 0;
> >          int cowflag = 0;
> > -   char c;
> > + int c;
> >          pid_t pid = 0;
> >          void *expected_addr = NULL;
> >          struct sembuf sembuffer;

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